It was the day when the leaves of London's plane trees seemed to have turned brown overnight, as if by mutual consent, and a cooler breeze blew through the ancient streets. Autumn had come and, with it, the end of a symphony of sport in two majestic movements. But not before a joyous coda, in the form of a celebratory parade, had sealed the memories of all the marvellous deeds of the past six weeks.

The bankers got the first glimpse, their ranks of pale blue shirts cramming the streets outside the temples of mammon as the parade of Britain's Olympic and Paralympic athletes set off from in front of the Mansion House, preceded by carnival paper lions and a high-stepping band.

Past St Paul's the 21 floats went, where Baron Pierre de Coubertin, the founder of the modern Olympics, is said to have listened closely in 1908 as a preacher advocated the taking part over the winning. Along Fleet Street, down the Strand and into Trafalgar Square, pavements and windows crowded with those thrilled by the sight of the entire dramatis personae, from Adlington to Zara, displaying their precious medals and their very best smiles.

All the heroes were present, along with those whose heroism was restricted to the considerable satisfaction of having taken part, every one of them now little lower than the angels in the nation's esteem.

Mo Farah, the favourite of all favourites, responded to calls for his famous Mo-Bot until his arms ached. The cheers rang out for Ellie Simmonds and Sir Chris Hoy, Laura Robson and David Weir, Hannah Cockroft and Ben Ainslie, Beth Tweddle and Peter Norfolk, the 51-year-old wheelchair tennis doubles champion.

A week earlier Aled Davies, the young Welshman with Paralympic gold and silver medals for discus and shot put around his neck, had looked astonished when 80,000 people roared their welcome as he was introduced on the first morning in the stadium; now he seemed quite accustomed to such unfettered adoration.

Only Bradley Wiggins and Andy Murray, both with pressing business elsewhere, were conspicuous by their absence.

In Trafalgar Square we thronged at the foot of Lord Nelson's great column, watching events on a big screen as the procession made its way towards us. Few could check another tear as Martine Wright, who lost her legs in the 7/7 atrocities and went on to represent her country in the sitting volleyball competition, struggled to hold back her own emotion during an interview conducted by the retired Olympic runner Iwan Thomas. Thomas hugged his interviewee at the conclusion of their conversation, and never has a rule of journalistic etiquette been more justifiably cast aside.

Two hours after setting off, the first of the floats reached the Mall, where the 700 athletes were greeted by a more variegated gathering, dominated by representatives of the volunteers now standing cheek by jowl with the armed forces who had come to the rescue when private enterprise failed to secure the gates of the Games.

Weirdly, the biggest cheer of all from those watching on the big screens was reserved for Boris Johnson, glimpsed midway through what seemed to be an attempt to high-five everyone out on the streets of London before taking his place next to David Cameron in the tribune of honour. He is clearly unstoppable now.

Perhaps we were given a clue that these Games were going to work in a rather surprising way when something as simple as the countdown to Danny Boyle's opening ceremony turned out to be such a witty and imaginative montage. An event that took its epigraphs from Shakespeare and Stephen Hawking became a festival of art and science as well as sport.

There will be no reliable estimate of the number of people who emerged to cheer the athletes and everything they represented. But it was a lot, and they formed a reminder that such large crowds do not usually turn out to cheer for the wrong side – on behalf of the poll tax, say, or for a morally questionable foreign war.

But it is probably best not to invest too much hope for a better world in a mere festival of sport: those Rapier ground-to-air missiles currently being removed from Blackheath Common and Shooters Hill are unlikely to be turned into ploughshares, or racing wheelchairs, any time soon.

The parade ended with an air display. There were speeches to come, but no one really needed any more words, even from Boris, as the streamers of red, white and blue smoke from the nine jets of the Red Arrows drifted and dispersed on the south-westerly air currents, blending with the pale grey clouds like a Turner canvas from the National Gallery below.

A moment of visual poetry, soon to melt away, unlike the memories that will brighten the bleaker days ahead.